FIELD OF THE INVENTION
The invention relates to a method for operating an anti-theft system for a motor vehicle, and to an anti-theft system operating according to the method, especially a locking system for doors of a motor vehicle and an immobilizer by which starting of the engine is enabled upon authorization.
An anti-theft system which is known from U.S. Pat. No. 5,053,774 has a transceiver disposed in a motor vehicle, that transmits a question code signal. A portable transponder receives the question code signal when it is located in the vicinity of the transceiver. A piece of code information is thereupon transmitted back to the transceiver and evaluated in she transceiver.
However, in such an anti-theft system, it can happen that no code signal is detected by the transceiver despite a properly functioning transponder. That happens if an operating point of the system is shifted far enough that it is in a so-called zero position, because of component tolerances or the effects of temperature.